An output circuit configured to switch a voltage of an output terminal between a ground potential and a power source potential (power source voltage) is known. A typical output circuit includes two switching elements connected serially between a ground and a power source, and a midpoint of this serial connection is connected with the output terminal. Hereinbelow, for the convenience of explanation, of two switching elements having a midpoint therebetween connected to an output terminal, the switching element on a high-potential side will be termed an upper switching element and the switching element on a low-potential side will be termed a lower switching element. When the upper switching element is maintained in an on-state and the lower switching element is maintained in an off-state, the output terminal is maintained at a power source voltage. When the upper switching element is switched off and the lower switching element is switched on, the output terminal is switched to a ground potential. A signal outputted from the output terminal is therefore a pulse signal having a LOW level being at the ground potential and a HIGH level being at the power source voltage.
Generally, a switching element of a p-channel type is used as the upper switching element and a switching element of a n-channel type is used as the lower switching element. The switching element of the p-channel type is switched between on and off by a pulse signal with a voltage amplitude that is lower than the power source voltage with a potential of a positive electrode of the switching element as a reference. The switching element of the n-channel type is switched between on and off by an input pulse signal with a voltage amplitude that is lower than the power source voltage with a potential of a negative electrode of the switching element as a reference. A “positive electrode of a switching element” refers to an electrode located on an input side where current flows in (thus a drain electrode in a case of a field effect transistor of the n-channel type), and a “negative electrode of the switching element” refers to an electrode on an output side where the current flows out (thus a source electrode in the case of the field effect transistor of the n-channel type).
In a case with an output circuit supplied with an input pulse signal with a low voltage with a ground potential as a reference, on/off control of its lower switching element can be executed by inputting the input pulse signal directly to a gate of the lower switching element of the n-channel type. On the other hand, for gate control of a switching element of the p-channel type, the gate control of its upper switching element must be executed by generating a signal that intensified the HIGH level of the input pulse signal to the power source voltage by using a level conversion circuit. An example of the level conversion circuit is described in JP 2006-94301 A (Patent Literature 1). The level conversion circuit requires a plurality of elements. In the level conversion circuit of Patent Literature 1, four transistors are required. A serial connection that uses a MOS (Metal-Oxide-Semiconductor) transistor of the p-channel type as its upper switching element and a MOS transistor of the n-channel type as its lower switching element is called a CMOS (Complementary MOS) circuit, and such is widely used (e.g., see Patent Literature 1).
In an output circuit that uses a serial connection of two switching elements on an output side, current may flow directly from a power source to a ground upon when on/off of upper and lower switching elements switch. Such current is called “through-current”. The circuit could be damaged with large through-current. An output circuit described in JP 2014-27515 A (Patent Literature 2) switches one of its switching elements from on to off, after which it switches another switching element from off to on responsive to a turnoff signal of the one of the switching elements. By doing so, it avoids an occurrence of a period during which both switching elements are turned on, thereby suppressing through-current.